As an information output apparatus in a wordprocessor, personal computer, facsimile apparatus, and the like, a printing apparatus which prints information such as a desired character or image on a sheet-like printing medium such as a paper sheet or film widely adopts a serial printing method of printing by reciprocal scanning in a direction perpendicular to the feed direction of a printing medium such as a paper sheet because this method can achieve cost reduction and easy downsizing.
The structure of a printhead used in such a printing apparatus will be explained by exemplifying a printhead complying with an inkjet method of printing using thermal energy. In the inkjet printhead, a heating element (heater) is arranged as a printing element at a portion communicating with an orifice (nozzle) for discharging ink droplets. The inkjet printhead prints by supplying a current to the heating element to generate heat, and bubbling ink to discharge ink droplets. This printhead makes it easy to arrange many orifices and heating elements (heaters) at high densities, and can obtain a high-resolution printed image.
In order to print by such a printhead at a high speed, it is desirable to simultaneously drive heaters as many as possible. However, the number of simultaneously drivable heaters is limited because the current supply capability of the power supply is limited, and the voltage drop by the parasitic resistance of a wiring line increases with an increase in current and inhibits supply of desired energy to the heater. From this, a plurality of heaters are divided into groups, and heaters within each group are driven (time division driving) with a time lag so as not to simultaneously drive them, suppressing the maximum value of a current which flows instantaneously.
An example of a circuit configuration which performs this driving is disclosed in, e.g., U.S. Pat. No. 6,520,613 (Japanese Patent Laid-Open No. 9-327914).
The circuit configuration disclosed in U.S. Pat. No. 6,520,613 (Japanese Patent Laid-Open No. 9-327914) performs matrix driving of selecting an arbitrary heater on the basis of the ANDs between outputs from registers for storing M data and N block selection signals when M×N heaters are to be driven for M heaters N times in time division. This configuration can reduce the circuit scale, and hardly malfunctions because data is transferred in time division.
FIG. 7 is a circuit diagram showing an example of the configuration of a driving circuit on an element board. In FIG. 7, reference numerals 101 denote heaters serving as printing elements; 102, transistors which drive the respective heaters; 103 and 104, AND circuits which AND logical signal inputs; 105, an X to N decoder which decodes an X-bit block control signal supplied from a printer main body and selects one of N block selection lines; and 106, a shift register+latch circuit which stores, in synchronism with a CLK signal, the X-bit block control signal transferred in a serial format from the printer main body and latches the block control signal by an LT signal.
N heaters 101, N transistors 102, and N AND circuits 103 and 104 form one group G1. The heaters 101, transistors 102, and AND circuits 103 and 104 are divided for N each into M groups G1 to GM. Reference numeral 1001 denotes a shift register+latch circuit including an M-bit shift register which sequentially stores printing data serially transferred in synchronism with the clock signal CLK supplied from the printer main body, and a latch circuit which latches serial data in accordance with the latch signal LT. M data signal lines 1002 run from the shift register+latch circuit 1001.
N block selection lines 107 are respectively connected to the inputs of the N AND circuits 104 which form a corresponding one of the groups G1 to GM. The other inputs of the AND circuits 104 are commonly connected within each group, and data signal lines are connected to the commonly connected wiring lines.
The operation of the driving circuit in FIG. 7 will be explained with reference to the timing chart of FIG. 8. The timing chart in FIG. 8 corresponds to one sequence (one discharge cycle) during which an arbitrary heater can be selected once from M×N heaters. That is, a cycle until the same heater is so selected as to be able to drive it again is defined as one cycle.
M-bit data corresponding to image data are serially transferred to the shift register+latch circuit 1001 by a DATA signal synchronized with the clock signal CLK. When the latch signal LT changes to “High” (high level), the input serial data are latched and output to the data lines 1002. The timings of the M data lines 1002 correspond to a DATAOUT signal in FIG. 8, and an arbitrary data line corresponding to image data among the M data lines changes to “High”.
Similarly, an X-bit block control signal is also serially transferred to the shift register+latch circuit 106 in synchronism with the clock signal CLK. When the latch signal LT changes to “High”, the X-bit block control signal is held by the decoder 105. The output timing from the decoder 105 to the block selection lines 107 corresponds to the timing of a block enable signal BE (FIG. 8) for selecting a block. The X-bit block control signal selects one of N outputs from the output lines 107, and the selected output changes to “High”.
Of M driving circuits commonly connected to one block selection line, an arbitrary heater for which DATAOUT changes to “High” is selected by the AND circuit. A current I flows through the selected heater in accordance with an HE signal, driving the heater.
This operation is sequentially repeated N times. M×N heaters are driven for M heaters N times in time division, and all the heaters can be selected in accordance with image data.
More specifically, M×N heaters are divided into M groups each formed from N heaters. Heaters within each group are controlled so that one sequence is divided by N so as not to simultaneously drive two or more heaters and M-bit image data are simultaneously printed within the divided time.
A layout method of efficiently laying out the driving circuit in FIG. 7 on an element board formed from a semiconductor base plate is disclosed in, e.g., Japanese Patent Laid-Open No. 11-300973.
FIG. 9 shows an example of laying out the circuit in FIG. 7 on an element board. Ink which is supplied from the lower surface of the element board via an ink supply port 701 at the center of the element board is supplied via the supply port onto the upper surface of the element board having heaters. The heaters generate heat to bubble ink, and as a result, ink supplied to the heaters is discharged in a direction perpendicular to the upper surface of the element board from nozzles formed on the upper surface of the element board.
In the layout shown in FIG. 9, heater groups 702 each having M×N heaters are symmetrically laid out in two arrays on the two sides of the ink supply port 701.
In FIG. 9, pad portions 709 and 710 for electrical connection to the apparatus main body are laid out on the two sides (short sides) in a direction crossing to the array direction of the heater group 702 on the element board. Shift registers+latches+decoder circuits 707 and shift registers+latch circuits 708 are interposed between the pad portions, and the heaters and driving circuit groups 703 and 704. Data output lines 705 running from the shift registers+latch circuits 708 and block selection lines 706 running from the shift registers+latches+decoder circuits 707 are laid out parallel to the heater groups 702. Data output lines 705 are formed from M data lines, and block selection lines 706 are formed from N block selection lines.
The correspondence between building components in the circuit diagram of FIG. 7 and regions in the layout of FIG. 9 will be explained. The heaters 101 are formed in the region 702; the transistors 102, in the region 703; the AND circuits 103 and 104, in the region 704; the data lines 1002, in the region 705; the block selection lines 107, in the region 706; the shift register+latch circuit 106 and decoder 105, in the region 707; and the shift register+latch circuit 1001, in the region 708.
As the number of printing elements (heaters) of the printhead increases for meeting demands for higher image qualities and higher speeds, the following problems arise.
When M×N heaters are matrix-driven, the number of wiring lines for either or both of the M data lines and N block selection lines must be increased in accordance with an increase in the number of heaters.
At this time, if the number of the heaters in one block N which determines the driving frequency of the heaters increases, ink discharging frequency for one nozzle is decreases, and hence the number N cannot increase. For performing high speed printing by increasing the number of nozzles, it is required to increase the number M which corresponds to the number of groups and represents the number of data lines and to increase the number of nozzles driven at the same time. As a result, the length of the short side of data lines wiring region 705 extending parallel to the heater array would increase in the circuit layout on the element board.
In general, heaters are laid out along the ink supply port, and an element board having many heaters has a rectangular shape long in the heater array direction and short in a crossing direction in order to effectively utilize the area of the element board.
If the short side of the wiring region parallel to the heater array becomes longer along with an increase in the number of heaters, the short side of the rectangular element board also becomes longer.
A circuit on the element board is built in a semiconductor wafer serving as a base plate (substrate). In order to reduce the cost of the element board, the area of the element board must be reduced to increase the number of element boards formed from one wafer.
However, as the short side of the rectangular plate-like element board (element substrate) becomes longer, the area of the element board increases, the number of element boards formed from one wafer greatly decreases, and the cost of one element board rises.